U.S. patent number 8,691,135 [Application Number 13/154,336] was granted by the patent office on 2014-04-08 for method of forming a film of novel composition for a dosimeter.
This patent grant is currently assigned to King Abdulaziz City for Science and Technology (KACST). The grantee listed for this patent is Ahmed A Basfar, Khalid A Raba'eh. Invention is credited to Ahmed A Basfar, Khalid A Raba'eh.
United States Patent |
8,691,135 |
Basfar , et al. |
April 8, 2014 |
Method of forming a film of novel composition for a dosimeter
Abstract
A tetrazolium bromide dye, e.g.,
3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT),
to be used as a high dose solution dosimeter is disclosed. The dose
response of MTT solution dosimeter increases strongly with increase
of absorbed dose up to 1 kGy. In order to increase the dose range
and for ease of handling the present dosimeter as routine
dosimeter, MTT-polyvinyl alcohol (PVA) film dosimeter is used. The
dose response of MTT-PVA film dosimeters increases strongly with
increase of absorbed dose up to 25 kGy. Polyvinyl butyral (PVB) as
a polymer for making a film provides more stability at higher
temperatures and humidity levels and less calibration is required.
The dose response of MTT-PVB film dosimeters is effective with
absorbed dose of up to 100 kGy. The effects of irradiation
temperature, relative humidity, dose rate and the stability of the
response of the films after irradiation were investigated and found
that these films could be used as a routine dosimeter in industrial
irradiation processing measurements.
Inventors: |
Basfar; Ahmed A (Riyadh,
SA), Raba'eh; Khalid A (Zarqa, JO) |
Applicant: |
Name |
City |
State |
Country |
Type |
Basfar; Ahmed A
Raba'eh; Khalid A |
Riyadh
Zarqa |
N/A
N/A |
SA
JO |
|
|
Assignee: |
King Abdulaziz City for Science and
Technology (KACST) (Riyadh, SA)
|
Family
ID: |
44655462 |
Appl.
No.: |
13/154,336 |
Filed: |
June 6, 2011 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20110233815 A1 |
Sep 29, 2011 |
|
Current U.S.
Class: |
264/299; 436/166;
436/164; 264/160 |
Current CPC
Class: |
C08J
3/02 (20130101); C08K 5/3472 (20130101); C08K
5/47 (20130101); C08K 5/47 (20130101); C08L
29/04 (20130101); C08K 5/47 (20130101); C08L
29/14 (20130101); C08J 2329/14 (20130101); C08J
2329/04 (20130101) |
Current International
Class: |
B29C
39/00 (20060101); G01N 21/75 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
AK. Pikaev, Z.K. Kriminskaya, Use of tetrazolium salts in dosimetry
of ionizing radiation, Radiation Physics and Chemistry, vol. 52,
Issues 1-6, Jun. 1998, pp. 555-561, ISSN 0969-806X,
http://dx.doi.org/10.1016/S0969-806X(98)00094-2.
(http://www.sciencedirect.com/science/article/pii/S0969806X98000942).
cited by examiner .
Sharpe et al., The effect of irradiation temperatures between
ambient and 80C on the response of alanine dosimeters, Radiation
Physics and Chemistry, 78(2009) pp. 473-475. cited by applicant
.
Levine et al., Temperature and Humidity Effects on the Gamma-Ray
Response and Stability of Plastic and Dyed Plastic Dosimeters,
Radiat. Phys. Chem. vol. 14, pp. 551-574. cited by
applicant.
|
Primary Examiner: Schiffman; Benjamin
Attorney, Agent or Firm: Kadambi; Geeta Riddhi IP LLC
Claims
What is claimed is:
1. A process, comprising: dissolving a tetrazolium bromide dye to
make a solution; dissolving a polymer solution using a solvent;
mixing the tetrazolium dye and the polymer solution to make a film
for measuring an irradiation heating the solvent to 80.degree. C.
to dissolve the polymer to make the polymer solution; stirring the
polymer solution using a magnetic stirrer for four hours; cooling
the polymer solution to room temperature; adding the tetrazolium
dye at a 1-5 mM concentration range to the polymer solution to make
a mixture; stirring the mixture of polymer solution and tetrazolium
bromide dye solution for 24 hours; pouring the mixture on a flat
glass plate to form a uniform film layer of a specific thickness;
drying the film till a constant weight for the film is obtained;
cutting the film to a specific dimension for further use to measure
irradiation; and storing the film in black plastic to protect from
light, moisture and dust.
2. The process of claim 1, wherein the tetrazolium bromide dye is
3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide
(MTT).
3. The process of claim 1, wherein the polymer to make the film for
a dosimeter is at least one of a polyvinyl alcohol and polyvinyl
butyral.
4. The process of claim 1, wherein the solvent is at least one of
an ethanol and distilled water.
5. The process of claim 1, wherein the specific thickness is
between 55-65 .mu.m.
6. A method, comprising: heating a solvent to 50.degree. C. to
dissolve a polymer to make a polymer solution; stirring the polymer
solution using a magnetic stirrer for four hours; cooling the
polymer solution to room temperature; adding a tetrazolium dye at a
1-5 mM concentration range to make a mixture; stirring the mixture
of the polymer solution and the tertrazolium dye solution for 24
hours; pouring the mixture on a flat glass plate to form a uniform
film layer of a specific thickness; wherein the specific thickness
is between 240-260 .mu.m; drying the uniform film layer till a
constant weight for a film is obtained; cutting the film to a
specific dimension for further use to measure irradiation using a
dosimeter; and storing the film in black plastic to protect from
light, moisture and dust.
7. The method of claim 6, further comprising: optimizing the film
at least for one of a irradiation temperature, stability, relative
humidity and dose rate.
8. The method of claim 6, wherein the tetrazolium bromide dye is
3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide
(MTT).
9. The method of claim 6, wherein the polymer to make the film for
the dosimeter is at least one of a polyvinyl alcohol and polyvinyl
butyral.
10. The method of claim 6, wherein the solvent is at least one of
an ethanol and distilled water.
Description
FIELD OF TECHNOLOGY
The present disclosure relates to a novel composition and film to
be used for dosimeter and Radio-chromic dosimeter (radiation
induced coloration) for use in high dose radiation processing such
as sterilization, food irradiation, agriculture, and polymers
treatment. More specifically method of making Radio-chromic
solution dosimeters, Polyvinyl alcohol (PVA) film dosimeters and
polyvinyl butyral (PVB) film dosimeters containing novel
composition of 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium
bromide (MTT).
BACKGROUND
The energy imparted to matter by ionizing radiation per unit mass
of irradiated material at the point of interest is called the
`absorbed dose` or dose and the unit is given in gray (Gy) or J/kg.
The dose can be calculated by knowing the energy of the radiation
and the composition of the medium, which then leads to the
formation of dosimeters. A dosimeter is defined as a device that
when irradiated, exhibits a quantifiable and reproducible change in
physical or chemical property of the device which can be related to
the dose in a given material using appropriate analytical
techniques.
Dosimetry plays an important role in process control in irradiation
facility where documents are required to assure that all the
factors which might influence the level of uncertainty in absorbed
dose estimation, and precautions should be taken to minimize the
uncertainties (ASTM. Standard Guide for Performance
Characterization of Dosimeters and dosimetry Systems for Use in
Radiation Processing. ASTM E2701). The importance of dosimetry is
emphasized in the standards on radiation sterilization which are
currently drafted by the European standards organization CEN and by
the international standards organization ISO. In both standards,
dosimetry plays key roles in characterization of the facility, in
qualification of the process and in routine process control. As a
function of the work on the standards, several issues are now
receiving major attention. These include traceability and
uncertainty limits of the dose measurements, calibration
procedures, environmental influence and combination of influence
factors such as dose rate and temperature. The increased attention
to these factors has increased the demands on existing dosimeter
systems, and need for more sensitive chemical composition to help
these dosimeters.
SUMMARY
The present disclosure describes a composition, process and method
for a new solution and a film to be used as dosimeters. More
specifically, as an embodiment, a radio-chromic dosimeter for
radiation processing especially in food irradiation and
sterilization of medical disposables are disclosed. In one
embodiment, a composition for a new type of dye comprises of
3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT)
solution. MTT dye is heterocyclic organic compound, which upon
irradiation yield highly colored water insoluble formazans due to
radiolytic reduction of these compounds by hydrated electrons or
hydroxyalkyl radicals. In one embodiment, the colorless and
transparent form of MTT solution undergoes a permanent color change
after exposure to high irradiation dose. In another embodiment,
various concentrations of the dye in vials as dosimeter solution
are optimized for irradiation dose response.
In another embodiment, a composition of a tetrazolium dye solution,
a polymer solution and a solvent is disclosed. In another
embodiment, polyvinyl alcohol is used as a polymer to make the
dosimeter film using a solvent. In another embodiment, polyvinyl
butyral is used as a polymer to make the dosimeter film using a
solvent. MTT, in one embodiment is mixed with the polymer to form a
film. MTT-polyvinyl alcohol (MTT-PVA) film dosimeters and MTT
polyvinyl butyral (MTT-PVB) film dosimeters are disclosed as
another embodiment.
In one embodiment, both the solution and film dosimeters were
prepared by adding variable concentrations of MTT dye using ethanol
as solvent. In another embodiment, the dosimeters were irradiated
with .gamma.-ray from .sup.60Co source up to 1 kGy for MTT solution
dosimetrs, 25 kGy for MTT-PVA films and 100 kGy for MTT-PVB films.
UV/VIS spectrophotometry was used to investigate the optical
density of unirradiated and irradiated films in terms of absorbance
at the range 350-650 nm, more specifically 560 nm.
In one embodiment, dose sensitivity of solution and films of MTT
dosimeters was optimized and observed that it increased
significantly with increase of concentration of MTT dye. In one
embodiment, the effects of irradiation temperature, humidity, dose
rate and the stability of the response of the films after
irradiation were optimized. In one embodiment, the influence of
irradiation temperature and humidity on the performance of the film
was reduced significantly due to the use of PVB as a binder
containing MTT dye.
In another embodiment, a method of use of the MTT solution, MTT-PVA
film and MTT-PVB film as a dosimeter for irradiation measurement is
disclosed. In another embodiment, an optimal thickness of the
MTT-PVA film and MTT-PVB film is disclosed.
BRIEF DESCRIPTION OF FIGURES
FIG. 1 Absorbance at 560 nm of 0.1, 0.2, and 0.3 mM of MTT solution
dosimeter as a function of absorbed dose.
FIG. 2 Absorbance of 0.3 mM of MTT solution dosimeter normalized
with respect to that at an irradiation temperature of 10.degree. C.
as a function of irradiation temperature.
FIG. 3 Absorbance of 0.3 mM of MTT solution dosimeter with
different pH levels irradiated at 25.degree. C. to 500 Gy.
FIG. 4 Absorbance of irradiated 0.3 mM of MTT solution dosimeter to
500 Gy as a function of storage time, (a) hours unit and (b)
days.
FIG. 5 Specific absorbance at 560 nm of 1, 3, and 5 mM of MTT-PVA
film dosimeter as a function of absorbed dose
FIG. 6 Specific absorbance of 5 mM of MTT-PVA film dosimeters
normalized with respect to that at an irradiation temperature of
10.degree. C. as a function of irradiation temperature for (a) 10
kGy and (b) 20 kGy.
FIG. 7 Specific absorbance of 5 mM of MTT-PVA film dosimeter
normalized with respect to that at 12% relative humidity at (a) 10
kGy and (b) 20 kGy.
FIG. 8 Specific absorbance of irradiated 5 mM of MTT-PVA film
dosimeter for different absorbed doses.
FIG. 9 Specific absorbance of un-irradiated 5 mM of MTT-PVA film
dosimeter in the dark as a function of storage time.
FIG. 10 Specific absorbance of un-irradiated 5 mM of MTT-PVA film
dosimeters under fluorescent light as a function of storage time,
(a) hours unit and (b) days.
FIG. 11 Specific absorbance of 5 mM of MTT-PVA film dosimeter
irradiated with gamma ray and with electron beam to different
absorbed doses.
FIG. 12 Specific absorbance at 560 nm of 1, 2.5 and 5 mM of MTT-PVB
film dosimeter as a function of absorbed dose.
FIG. 13 Specific absorbance of 5 mM of MTT-PVB film dosimeter
normalized with respect to that at an irradiation temperature of
10.degree. C. as a function of irradiation temperature for (a) 10
kGy and (b) 20 kGy.
FIG. 14 Specific absorbance of 5 mM of MTT-PVB film dosimeter
normalized with respect to that at 12% relative humidity at (a) 10
kGy and (b) 20 kGy.
FIG. 15 Specific absorbance of irradiated 5 mM of MTT-PVB film
dosimeter for different absorbed doses.
FIG. 16 Specific absorbance of un-irradiated 5 mM of MTT-PVB film
dosimeter in the dark as a function of storage time.
FIG. 17 Specific absorbance of un-irradiated 5 mM of MTT-PVB film
dosimeter under fluorescent light as a function of storage time,
(a) hours and (b) days.
FIG. 18 Specific absorbance of 5 mM of MTT-PVB film dosimeter
irradiated with gamma ray and with electron beam to different
absorbed doses.
DETAILED DESCRIPTION
Radio chromic films are one category of dosimeters which depend on
permanent change in color when exposed to high-dose radiation
(Holm, N. W. Berry, R. J. (Eds.), 1970a. Film, Dyes and
Photographic Systems, Manual on Radiation Dosimetry, Marcel Dekker,
New York and Holm, N. W. Berry, R. J. (Eds.), 1970b Film,
Radio-chromic Dye-Cyanide Dosimeters, Manual on Radiation
Dosimetry, Marcel Dekker, New York). The advantage of radio-chromic
film compared to traditional point measurements dosimeters such as
ionization chamber is the ability to produce a two-dimensional (2D)
optical density map, with appropriate corrections, this can be
converted to a 2D dose map. In addition, these dosimeters have a
very high spatial resolution and relatively low-energy spectral
sensitivity.
Tetrazolium salts are chemical compounds used long time ago in
biological applications to highlight reduction chemical reactions
which take place in life cells especially reactions with enzymes in
the biological applications. These are dyes which change their
colors when chemical reduction reactions take place. Most of these
tetrazolium salts are colorless or have very light yellow colors
which change to blue or violet colors after chemical reduction
reactions, when the chemical form of tetrazolium changes to
formazan. Formazans are very stable in color and insoluble in
water.
A new radio-chromic dosimeters composition based on tetrazolium dye
(MTT) solution dosimeters, MTT-PVA and MTT-PVB film dosimeters are
disclosed in the instant application. The solution of MTT dye was
prepared by dissolving different weights of MTT (EMD, USA) in 96%
ethanol to obtain different concentrations of MTT i.e. 0.1, 0.2 and
0.3 mM. The solution was stirred at room temperature for 3 hours to
ensure a homogenous dye solution. The solutions were kept in 3 ml
sealed glass ampoules tubes and stored in the dark at room
temperature (23.+-.1.degree. C.). The pH of the solutions was set
with HCl and NaOH, respectively.
In one embodiment, as a method, dye solutions were irradiated with
1.25 MeV gamma-ray from .sup.60Co source Model GC-220 supplied by
MDS Nordion, Canada at a mean dose rate of 8.6 kGy/h which
connected to air chiller system, Turbo-Jet (Kinetics, USA) in order
to monitor the temperature during irradiation. The dose rate of the
source was calibrated using ferrous sulphate dosimeter or fricke
dosimeter (ASTM Standard Practice E1026, 2004). At each dose point,
three films were sandwiched together between two polystyrene (PS)
blocks with 6 mm thickness in order to establish secondary charged
particle equilibrium and the average is reported. The PS blocks
were positioned at the center where absorbed dose is uniform.
Electron beam irradiation was conducted at Sure Beam Middle East
Corp. (SBE) irradiation facility in Riyadh, Saudi Arabia with two
electron beam accelerators positioned vertically (tower and bit) at
dose rate of 1 kGy/s and at room temperature. The electron beam
parameters are listed in Table 1 below. Alanine pellet dosimeters
were used as a reference dosimeter irradiated along invented films
in accordance with ISO/ASTM 51607. Alanine pellet dosimeters are
traceable to National Institute of Standard and Technology (NIST)
in USA. Alanine dosimeters are measured by E-Scan EPR spectrometer
(Bruker Biospin Company, Germany). Similar to gamma irradiation,
three films were sandwiched together between two PS blocks in order
to maintain electronic equilibrium during EB irradiation. The PS
blocks were placed on the tray of conveyor system of EB
accelerator
TABLE-US-00001 TABLE 1 Electron beam system operating parameters
Parameter Tower Pit Beam Energy (MeV) 10 10 Average Beam Current
(mA) 1.43 1.6 Average Beam Power (kW) 14.3 16 Scan Magnet Current
(A) 233 200 Scan Width (cm) 120 120 Pulse Per Scan 64 64 Scan
Frequency (Hz) 5.05 5.26 Pulse Repetition Rate (Hz) 288 302
UV/VIS spectrophotometer is used to measure the absorbance of
spectra of radiation in the near infrared (700-1100 nm), visible
(350-700 nm) and ultra violet (190-350) nm regions. The absorption
spectra of irradiated MTT samples in the wavelength range from
350-650 nm were measured using UV/VIS spectrophotometer, model
Lambda 850, from Perkin-Elmer, USA. Three samples at each absorbed
dose were measured, but no significant differences in their
characteristics were found during measurements.
The effect of the dye concentrations on the response of the
dosimeter solutions was investigated at fixed irradiation
temperature (i.e. 25.+-.1.degree. C.) and at (pH=5.6). The dose
response curves were established in terms of change in absorption
peak measured at 560 nm versus the absorbed dose. FIG. 1. shows
that the dose response of different concentrations of MTT dye in
the dose range 100-1000 Gy. The dose response of MTT solution
increases linearly with increase of dose, which can be seen from an
increase of the individual relative absorbance-dose curve (see FIG.
1). As the dose increases, more hydrated electrons and free
radicals are generated leading to breakage of N--N.sup.+ bonds,
resulting in an increase in the formation of colored formazan. The
results show that dose response increases with increase of dye
concentration, indicating that MTT dosimeter solution containing
higher concentrations of the MTT dye are more suitable for high
dose dosimetry.
The effect of irradiation temperature of MTT solutions were
investigated by irradiating solution samples containing 0.3 mM MTT
dye to 500 Gy in the temperature range of 10-40.degree. C. A set of
three samples was used for each temperature. The variation in
absorbance of the samples was normalized with respect to that at an
irradiation temperature of 10.degree. C. (see FIG. 2). The results
show that MTT solution dosimeters are very sensitive to irradiation
temperature. Therefore, the response has to be corrected under
actual processing conditions.
The effect of pH on MTT solutions were investigated by irradiating
solution samples containing 0.3 mM MTT dye with different pH values
to 500 Gy at irradiation temperature of 25.+-.1.degree. C. A set of
three samples was used for each pH values. FIG. 3 shows that the
response of MTT solution dosimeters increases with increase of pH
values due to competition of H+ for the solvated electrons and the
instability of the dye.
The stability of MTT solution dosimeters was tested by irradiating
MTT solution containing 0.3 mM MTT dye to 500 Gy and storing under
normal laboratory conditions in the dark. A set of three samples
was used for each absorbed dose. The results show no change (less
than .+-.2%; 1.sigma.) in the absorbance of the MTT dosimeters up
to 6 days (see FIGS. 4 (a and b)).
In order to increase the dose range and ease of handling of
invented dosimeter as routine dosimeter, MTT-PVA film dosimeters
are described in this disclosure. Polyvinyl alcohol (PVA) solutions
were prepared by dissolving 7.2 g of PVA powder (Mw=108,000 g/M,
Polysciences Inc., USA) in 90 ml distilled water at temperature of
80.degree. C. The solution was magnetically stirred at this
temperature for 4 hours and then left to cool to room temperature.
After cooling to room temperature, PVA solution was divided into 30
ml samples. Then, different concentrations of MTT 1, 3 and 5 mM
were added to 30 ml PVA solution. Mixtures were stirred
continuously for 24 hours using a magnetic stirrer in order to
obtain a uniform mixed dye-PVA solution. MTT-PVA solutions were
poured onto a high levelled horizontal glass plates and dried at
room temperature for about 72 hours. Films were peeled off and cut
into 1.times.3 cm pieces, dried, stored and prepared for
irradiation. The drying is completed once the weight of the films
was constant. The films were protected from sunlight, fluorescent
light, moisture and dust by storing them in small paper envelop and
wrapping them with black plastic tape. The thickness of the film is
60.+-.3 .mu.m with a very good uniformity.
MTT-PVA films were irradiated with 1.25 MeV gamma-ray from
.sup.60Co source Model GC-220 supplied by MDS Nordion, Canada at a
mean dose rate of 8.6 kGy/h which is connected to an air chiller
system. Irradiations were conducted at room temperature. Three
samples were irradiated for each absorbed dose, but no significant
differences in their characteristics were found during
measurements.
A range of 12-75% relative humidity levels were used to study the
effect of humidity on the performance of MTT film dosimeters during
irradiation. These humidity levels were achieved using the
following saturated salt solutions: LiCl (12%),
MgCl.sub.2.times.6H.sub.2O (34%),
Mg(NO.sub.3).sub.2.times.6H.sub.2O (55%) and NaCl (75%) according
to the technique devised by (Levine, H., McLaughlin, W. L., Miller,
A., 1979. Temperature and humidity effects on the Gamma-ray
response and stability of plastic and dyed plastic dosimeters.
Radiat. Phys. Chem. 14, 551-574). The films were irradiated in a
given humidity environment and were kept in the same environment
for 3 days before irradiation to ensure equilibrium conditions.
The effect of the dye concentrations on the response of the
dosimeter films was investigated in different compositions of
MTT-PVA films. The dose response curves were established in terms
of change in absorption peak measured at 560 nm per thickness in mm
.DELTA.A (.DELTA.A=A.sub.x-A.sub.0) versus the absorbed dose, where
A.sub.x and A.sub.0 are absorbance values at 560 nm for irradiated
and un-irradiated films. Dose response of MTT-PVA films is shown in
FIG. 5.
The dose response of MTT-PVA film increases with increase of
absorbed dose, which can be seen from the increase of the
individual relative absorbance-dose curve (see FIG. 5). As the dose
increases, more hydrated electrons and free radicals are generated
leading to breakage of N--N.sup.+ bonds, resulting in an increase
in the formation of colored formazan. The results show that dose
response increases with increase of dye concentration, indicating
that MTT-PVA dosimeter films containing higher concentrations of
the MTT dye are more suitable for high dose dosimetry.
The effect of irradiation temperature of MTT-PVA films were
investigated by irradiating film samples containing 5 mM MTT dye to
10 kGy and 20 kGy in the temperature range of 10-40.degree. C. A
set of three films was used for each temperature. The variation in
absorbance of the films were normalized with respect to that at an
irradiation temperature of 10.degree. C. (see FIGS. 6 (a and b).
The results show that the response of MTT-PVA films increased
reasonably with increase of irradiation temperature.
The effect of humidity on the MTT-PVA film dosimeter was
investigated by storing film samples containing 5 mM MTT dye in
vials in different humidity levels (12%, 34%, 55% and 74% relative
humidity) for three days, then the films were irradiated in the
same vials to 10 and 20 kGy. A set of three films was used for each
vial. The variation in absorbance of the irradiated films (10 and
20 kGy) were normalized with respect to that at 12% relative
humidity (see FIGS. 7 (a and b). The results show that the response
of MTT-PVA films increased significantly with increase of relative
humidity.
The stability of MTT-PVA films were tested by measuring the
absorbance of films containing 5 mM MTT. MTT-PVA films were
irradiated to 5, 10 and 20 kGy and kept under normal laboratory
conditions in the dark. A set of three films was used for each
absorbed dose. The results show no change (less than .+-.5%;
1.sigma.) in the specific absorbance of the films up to 54 days
(see FIG. 8).
The stability of un-irradiated MTT-PVA film was also investigated
under dark up to 10 days and under fluorescent light up to 30 days
as shown in FIG. 9, and FIGS. 10 (a and b), respectively. The
results show no change (less than 6%; 1.sigma.) in the specific
absorbance of the un-irradiated films PVA films up to 10 days in
the dark. A significant change (more than 116%; 1.sigma.) in the
specific absorbance of the un-irradiated films PVA films up to 31
days under fluorescent light was observed.
The effect of dose rate on the response of MTT-PVA film dosimeters
was investigated using 1.25 MeV gamma-ray from .sup.60Co source at
a mean dose rate of 8.6 kGy/h and an electron beam accelerator at
mean dose rate of 1 kGy/s, relative humidity of 50% and at
temperature of 25.degree. C. for irradiation at absorbed doses of
10, 20, 30 and 40 kGy. Three dosimeters were irradiated at each
absorbed dose. It was found that there is no appreciable effect of
dose rate on MTT-PVA film dosimeters (see FIG. 11).
Polyvinyl alcohol has low threshold to react to high humidity. In
order to circumvent this problem, polyvinyl butyral (PVB) was used
in another embodiment. Polyvinyl butyral (PVB) solutions were
prepared by dissolving 15 g of PVB powder (Mw=36,000 g/M, Wacker,
USA) in 150 ml 96% ethanol at temperature of 50.degree. C. The
solution was magnetically stirred at this temperature for 4 hours
and then left to cool to room temperature. After cooling to room
temperature, PVB solution was divided into three parts. PVB
composites were prepared by dissolving different concentrations of
MTT (i.e. 1, 2.5 and 5 mM) in the three parts of PVB solutions,
respectively. Mixtures were stirred continuously for 24 hours using
a magnetic stirrer in order to obtain a uniformly dyed PVB
solution. MTT-PVB solutions were poured onto a highly leveled
horizontal glass plates and dried at room temperature for about 72
hours. Films were peeled off and cut into 1.times.3 cm pieces,
dried, stored and prepared for irradiation. The drying is completed
when the weight of the films is constant. The films were protected
from sunlight, fluorescent light, moisture and dust by storing them
in small paper envelop and wrapping them with black plastic tape.
The thickness of the film is 250.+-.10 .mu.m with a very good
uniformity. The irradiation of MTT-PVB films were carried out as
mentioned previously for MTT-PVA films.
The effect of the dye concentrations on the response of the film
dosimeter was investigated in different compositions of MTT-PVB
films. The dose response curves were established in terms of change
in absorption peak measured at 560 nm per thickness in mm versus
the absorbed dose. Dose response of MTT-PVB films is shown in FIG.
12. The dose response of MTT-PVB film increases with increase of
absorbed dose, which can be seen from an increase of the individual
relative absorbance-dose curve (see FIG. 12). As the dose
increases, more hydrated electrons and free radicals are generated
leading to breakage of N--N.sup.+ bonds, resulting in an increase
in the formation of colored formazan. The results show that dose
response increases with increase of dye concentration, indicating
that MTT-PVB film dosimeter containing higher concentrations of the
MTT dye are more suitable for high dose dosimetry. Previous study
of MTT-PVA films demonstrated that the dose response tended to
saturate after 20 kGy. Therefore, these new composites of MTT-PVB
film dosimeter with high dose range have more potential for high
dose applications
The effect of irradiation temperature of MTT-PVB films was
investigated by irradiating film samples containing 5 mM MTT dye to
10 kGy and 20 kGy in the temperature range of 10-40.degree. C. A
set of three films was used for each irradiation temperature. The
variation in absorbance of the films were normalized with respect
to that at an irradiation temperature of 10.degree. C. (see FIGS.
13 (a and b)). The results show that MTT-PVB films are less
sensitive to irradiation temperature than MTT-PVA films. The
response of MTT-PVB has to be corrected under actual processing
conditions (Sharpe, P. H. G., Miller, A., Sephton, J. P.,
Gouldstone, C. A., Bailey, M., Helt-Hansen, J. 2009. The effect of
irradiation temperatures between ambient and 80.degree. C. on the
response of alanine dosimeters. Radiat. Phys. Chem. 78,
473-475).
The effect of humidity on MTT-PVB film dosimeters were investigated
by storing film samples containing 5 mM MTT dye in vials in
different humidity levels (12%, 34%, 55% and 74% relative humidity)
for three days, then the films were irradiated in the same vials to
10 and 20 kGy. A set of three films was used for each humidity
level. The variation in absorbance of the irradiated films (10 and
20 kGy) were normalized with respect to that at 12% relative
humidity (see FIGS. 14 (a and b)). The results show that the dose
response of MTT-PVB film is not as sensitive to relative humidity
as MTT-PVA film.
The stability of MTT-PVB films were tested by measuring the
absorbance of films containing 5 mM MTT. MTT-PVB films were
irradiated to 10, 20 and 40 kGy and kept under normal laboratory
conditions in the dark. A set of three films was used for each
absorbed dose. The results show no change (less than .+-.2%;
1.sigma. for MTT-PVB) in the specific absorbance of the PVB up to
44 days (see FIG. 15). The stability of un-irradiated MTT-PVB films
were also investigated under dark up to 10 days and under
fluorescent light up to 31 days as shown in FIG. 16 and FIGS. 17 (a
and b). The results show no change (less than .+-.2%; 1.sigma. for
MTT-PVB) in the specific absorbance of the un-irradiated films PVB
up to 10 days in the dark. A significant change (more than .+-.88%;
1.sigma. for MTT-PVB) in the specific absorbance of the
un-irradiated PVB films up to 31 days under fluorescent light was
observed.
The effect of dose rate on the response of MTT-PVB film dosimeters
was investigated using 1.25 MeV gamma-ray from .sup.60Co source at
a mean dose rate of 8.6 kGy/h and an electron beam accelerator at a
mean dose rate of 1 kGy/s, relative humidity of 50% and at
temperature of 25.degree. C. for irradiation at absorbed dose of
10, 20, 30 and 40 kGy. Three dosimeters were irradiated for each
absorbed dose. It was found that there is no appreciable effect of
dose rate on MTT-PVB film dosimeters (see FIG. 18).
In addition, it will be appreciated that the various compositions,
films, solution composition in combination with films, method of
use for irradiation measurement, process of making the composition
and film disclosed herein may be embodied using means for achieving
the various irradiation dose response and results of irradiation.
Accordingly, the specification and drawings are to be regarded in
an illustrative rather than a restrictive sense.
* * * * *
References